Computer vision based methods for tracking multiple objects rely on the distinctive appearance and known motion models of objects to continuously locate and identify them in the scene. Generally, the fidelity of positional data generated by vision-based methods is high. However, when the objects being tracked move in clusters, it complicates the tracking process. Numerous techniques address the challenge of tracking objects undergoing occlusion. Such algorithms that attempt to resolve this problem are usually successful, providing the objects possess distinctive appearances and their motion is consistent. Nevertheless, in practice, objects may have similar appearances and their motion under occlusion may be unpredictable. Such situations occur in a team game (football, basketball, etc.) where players tend to huddle in clusters.
An alternative to vision-based tracking systems is to use RTLS technology. An RTLS is a locating technology designed to detect and track people as well as assets. It includes transponders (transmitter/responder components) attached to dynamic objects, portable or stationary readers (transceivers-transmitter/receiver-components), and a server application. An RTLS methodology spans various technologies including infrared, sound, ultrasound, Wi-Fi, radio frequency identification (RFID), Ultra Wideband, GPS, and Cellular. Each technology is better suited for a certain application depending on parameters such as power requirements, range, indoor versus outdoor applicability, spatial accuracy (granularity), latency, and data rate.
Essential to the RTLS is the transponder (tag) characteristic. Objects under tracking may be tagged by passive, semi-passive, or active tags. A passive transponder does not have a battery and, therefore, does not initiate a communication. It is empowered by the received signal and responds by reflecting this signal using a technique termed backscatter. The reflected signal is modulated with data stored in the tag's memory. The range of a passive tag (up to 100 meters) is a function of the reader's signal strength and the tag's antenna. It is physically small and light, without any processing capability, and, therefore, inexpensive. Just like passive transponders, semi-passive transponders do not initiate communication but use a backscatter technique to respond to the received signal. Nevertheless, they do have their own battery (up to a 10 year lifetime) which is used mainly to power environmental sensors, measuring temperature or motion, for example, or to increase operation range. Operational range and size are comparable to those of a passive transponder. On the other hand, active transponders are equipped with a battery (up to a 5 year lifetime) which is used to power their circuitry and generate transmission signals. Hence, active transponders can initiate communication periodically or when triggered by an attached sensor. However, frequent transmissions consume more energy and shorten battery life. Depending on the type of battery, an active transponder is physically larger than a passive transponder, its range can reach up to several hundred meters, and its processing capability is better as it may contain a computer chip.
Although RTLS is a promising and an emerging technology, it suffers from physical difficulties, including multipath fading, signal attenuation, limited data rate, latency, and, most importantly, the need to have multiple lines of sight (LOS). In some applications, an RTLS is required to identify and locate objects with high accuracy and precision. For example, in tracking players in a team game, the positional data of the players during live game broadcast is instrumental for real time annotation (telestration) and for computing the players' performance statistics. Since most of the time the players move around quickly and in close proximity to each other, meaningful tracking performance should be within an accuracy of less than one foot.
What is needed are improved methods for utilizing vision based technology and RTLS technology to track players in a game that are occluded or in a cluster.